1. Field of the Invention
This invention generally relates to a liquid crystal display device and, more particularly, to a horizontal electric field type liquid crystal display and pixel structure thereof.
2. Description of the Related Art
Liquid crystal display technologies can be divided into two categories: twisted nematic liquid crystal displays (TN-LCD) and horizontal electric field type liquid crystal displays, wherein the horizontal electric field type liquid crystal displays further include in-plan switching (IPS) mode liquid crystal displays and fringe field switching (FFS) mode liquid crystal displays. In TN-LCD, liquid crystal molecules rotate following the variation of a longitudinal electric field between two opposite glass substrates. In horizontal electric field type liquid crystal display, the common electrode and the pixel electrode are both formed on the thin film transistor array substrate to provide a transverse electric field such that liquid crystal molecules can rotate transversely following the variation of the transverse electric field. Compared with the TN-LCD, the horizontal electric field type liquid crystal display has a wider viewing angle so that the viewing angle problem of the liquid crystal display can be solved.
However, in horizontal electric field type liquid crystal display electric charges can gradually accumulate in the stray capacitance between gate lines and other components of the display with the pixel operation to generate stray electric field which can influence the distribution of the transverse electric field during the pixel operation such that the orientation of liquid crystal molecules close to the gate lines can deviate from the desired direction to cause light leakage in dark state. For example, FIG. 1A shows a pixel structure 9 of a conventional FFS mode liquid crystal display, and as mentioned above electric charges can accumulate in the stray capacitance between the gate line 91 and other components of the display when scan signals are transmitting in the gate line 91. The voltage variation of the stray capacitance can lead to the change of the stray electric field to influence the rotation of liquid crystal molecules close to the gate line 91 to cause the light leakage problem thereby decreasing the contrast of the display. FIG. 1B shows a pixel structure 9′ of a conventional IPS mode liquid crystal display in which a plurality of stripe pixel electrodes 92′ and common electrodes 93 are alternatively formed on a substrate. When a potential difference is formed between the pixel electrodes 92′ and the common electrodes 93, a transverse electric field can then be formed therebetween. Similarly, electric charges can accumulate in the stray capacitance between the gate line 91 and other components of the display due to the transmission of electric signals in the gate line 91 to influence the rotation of liquid crystal molecules close to the gate line 91.
Accordingly, it is necessary to provide a liquid crystal display device and pixel structure thereof that is able to solve or significantly improve the light leakage problem in the horizontal electric field type liquid crystal display so as to improve the contrast of the display.